The present invention relates to a control device with a snap function, including a support, a push-button mounted so as to move on the support so as to have a translation travel along one axis, and a spring element able to exert a reactive force on the push-button which passes through a maximum during the travel of the push-button. The invention also concerns a watch including a case and a control device of this type.
Such a control device, also called a snap action control device, can be used in particular to activate a contact strip of an electric switch, particularly to control functions of a portable electronic device. However, the push-button of such a device may also produce a purely mechanical command.
Such devices are used, for example, to control the stop and start functions of mechanical or electric chronograph watches. The snap function means that the push-button remains without effect as long as the pressure exerted does not exceed a limit value for the reactive force, then once the limit is exceeded, the devices abruptly changes state, since the pressure necessary to end the function is less than this limit value. It is thus possible to start or stop a counter with precision.
In such known watches, the parts assuring the snap function usually form part of the chronograph mechanism and are secured onto a bridge or the plate of the movement. The force to be overcome is generated by a jumper-spring type device, with a spring working by bending, which cooperates with a cam, as provided for example by Swiss Patent No. 642 220. Devices of this type require significant volume, which is a considerable handicap in a watch.
Making snap function push-buttons wherein this function is assured by a spring element mounted on the case or push-button has also been proposed. A solution of this kind is shown in Swiss Patent No. 629 647. In this document, the spring element is made by means of an annular part, which can be deformed radially, which slides over a cam surface and passes over a raised portion of said surface. Such a solution does not require much space, but it is difficult to control the trigger point and the force to be applied to assure the function.
Control devices using snap springs to generate a snap action are also known in the specific field of electric switches. A compact type of snap spring, illustrated for example in U.S. Pat. No. 4,234,769, is formed by a flexible straight strip which is held bent longitudinally by compression between two fixed stops. However, this spring has two stable positions and in a push button control, this requires an additional return spring. Another drawback is that the permanent compression requires quite a robust support which may constitute an inconvenient element in a small apparatus such as a watch.
These drawbacks may be partially overcome by incorporating the compression bent strip in a larger plate spring which forms a frame around it and which will itself be bent by the push-button for example as shown in U.S. Pat. No. 5,075,524. However, this system requires a relatively large course for the push-button and thus proves too cumbersome in an apparatus as small as a watch. Further, the securing of this spring element also requires a robust support and a certain space requirement.
One object of the present invention is to make a simple and compact control device having a snap function. Additionally, the device should be easy to manufacture and mount and reliable during operation.
The present invention therefore concerns, according to a first aspect, a control device with a snap function of the type indicated in the preamble, characterized in that the spring element includes an elongated sheet made of resilient material, inserted between the push-button and the support and having at least a median zone arranged in its central portion and at least a pair of support zones located at the ends of said sheet, the pair of support zones and the median zone being intended to abut one against the push-button and the other against the support so that the travel of the push-button tends to bend said sheet longitudinally, and in that said sheet has a bent or V-shaped cross section in the rest position.
One advantage of this arrangement is that the spring element does not need to be rigidly secured to the support, which thus does not have to be particularly robust. The support zones of the spring element need only be held at the correct place, for example by the push-button or as a result of a housing in which the element is freely encased.
In fact, the spring element does not need to be secured either to the support or to the push-button. Another advantage is that an element of this type can be very small, in particular not larger than the head of the push-button and that the device assembly can be manufactured and mounted at a very low price.
Preferably, in order to assure good working conditions for the push-button and the spring element, the latter includes, in its central portion, an orifice through which a push-button stem passes.
In a preferred embodiment, said pair of support zones is located on a concave face, and the median zone on a convex face of the spring element. Advantageously, the support abuts against the concave face and the push-button against the convex face.
In order to guarantee that the working conditions remain the same during the life of the product, it is desirable for the spring element to be positioned with respect to the support and the push-button. It therefore includes cut out portions in proximity to its opposite ends in contact with the push-button. Further, the latter is provided with protrusions engaged in these cut out portions to assure the relative positioning of the spring element and the push-button. The push-button itself may be guided in a conventional manner with respect to the support.
Good manufacturing conditions have been obtained when the shape of the spring element includes two plane walls connected to each other by a rounded portion. This structure further allows a clearly defined snap action to be guaranteed and the force to be applied to be well controlled, so that, for a same model, it is practically the same from one piece to another.
The present invention also relates to a watch provided with a case and a control device as defined hereinabove. In this watch, the case forms the support for the control device, the push-button includes a head arranged outside the case and a stem engaged in a hole in the case and opening out inside the case. The spring element is arranged in a recess of an outer face of the case and cooperates with the push-button head.
The thickness of watches has an important role from the aesthetic point of view. In order to reduce this thickness as much as possible while having push-buttons which are easy to handle, both the push-button head and the spring element of the control device can be of elongated, preferably oval shape.